Enabling the Read-Only Mode for ClickHouse Tables

Updated on 2024-10-09 GMT+08:00

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NOTE:

This topic is available for MRS 3.2.0 or later only.

Scenario

During data migration, one-click balancing, decommissioning and capacity reduction, ClickHouse allows you to set the only_allow_select_statement parameter for MergeTree series tables to enable SELECT operations instead of ALTER, RENAME, DROP, and INSERT operations.

Procedure for Enabling the Read-Only Mode of the ClickHouse Table

Install the client. For details, see Installing a Client.
Run the following commands to log in to the node where the client is installed as user root:

cd Client installation directory

source bigdata_env
Run the following command to authenticate the user if the cluster is in security mode (with Kerberos authentication enabled). Otherwise, skip this step.

kinit Component service user
NOTE:

The user must have the ClickHouse administrator permissions.
Run the proper client command to connect to the ClickHouse server.
- Normal mode
  clickhouse client --host IP address of the ClickHouse instance--user Username --password --port 9440 --secure
  
  Enter the user password.
- Security mode
  clickhouse client --host IP address of the ClickHouse instance--port 9440 --secure
NOTE:
- For a cluster in normal mode, the username is default. Alternatively, you can create an administrator using the open source ClickHouse web UI. Do not use the users created on FusionInsight Manager.
- To obtain the IP address of the ClickHouseServer instance, log in to FusionInsight Manager, choose Cluster > Services > ClickHouse, and click the Instance tab.
Run the following statement to set the table to read-only:

ALTER TABLE {table_name} MODIFY SETTING only_allow_select_statement = true;

Disabling the Read-Only Mode of the Table

Log in to the ClickHouse client by referring to 2 to 4.
Run the following statement to disable the read-only mode of the table:

ALTER TABLE {table_name} MODIFY SETTING only_allow_select_statement = false settings hw_internal_operation = true;

Parent topic: ClickHouse O&M Management

Previous topic: Collecting Dumping Logs of the ClickHouse System Tables

Next topic: Migrating Data Between ClickHouseServer Nodes in a Cluster

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